Today, image-based inspection systems are often employed for physical inspection of an object of interest. Such systems typically employ an optical- or x-ray-based source at a distance from an object of interest at which an area of the object is in focus. Additionally, many such systems currently employ a positioning mechanism whereby the distance between the imaging source and the object is adjustable so that the surface to be inspected may be brought into proper focus.
For example, x-ray laminography machines that are employed to inspect printed circuit boards (PCBs) for manufacturing defects often utilize such a mechanism to keep a small portion of the board under inspection near a focal plane. The position of the focal plane is determined by the location of an x-ray source and x-ray detector, which reside on opposite sides of the PCB under inspection. The area under inspection, which is roughly square in shape, is typically much smaller than the area of the PCB itself, and commonly on the order of one-quarter- to one-inch across.
Unfortunately, warping of the PCB may be of sufficient severity that some portion of the area being inspected may remain out of focus, forcing the use of an even smaller inspection area. As seen in FIG. 1, a warped PCB 100 may cause all but a small area on the top side of PCB 100 to reside outside of a depth of focus 110 of an optical or x-ray inspection system, resulting in a small area, defined by a narrow width 120, that may be inspected at any one time. The use of a reduced inspection area generally results in more inspection areas being necessary for each PCB, thereby resulting in a significantly longer inspection time required for each PCB and, consequently, a drastic reduction in PCB inspection throughput.
Additionally, the focus problems due to PCB warping can also cause the inspection system to falsely identify out-of-focus areas of the PCB under inspection as manufacturing defects, resulting in costs due to unnecessary additional testing or discarding of properly manufactured PCBs.
Such problems regarding a changing focal distance over the surface of an object is not limited to PCB x-ray laminography inspection machines. Other optical or x-ray-based viewing or inspection machines that employ only a focal length adjustment likely encounter the same difficulties with objects having a nonplanar structure to be viewed or inspected.
Therefore, from the foregoing, a new positioning adjustment mechanism that allows more area of an object under inspection to reside within the depth of focus, thus allowing for a greater inspection area and, thus, higher inspection throughput, would be advantageous.
Embodiments of the invention, to be discussed in detail below, allow an object under inspection to be rotated and translated in such a manner that more of the object will reside within the depth of focus of an image-based inspection machine. Continuing with the PCB example in FIG. 2, if the warped PCB 100 (from FIG. 1) is rotated about an axis within the plane generally defined by depth of focus 110, more area of the top surface of PCB 100, as defined by larger width 200, lies within depth of focus 110. Since warping or other irregularities in an object under inspection can occur in any direction along a surface of the object, the ability of an adjustment mechanism to rotate the object about any two orthogonal horizontal axes to account for any such irregularities is desirable.
Assuming that a focal plane of an inspection system is oriented horizontally, as shown in FIGS. 1 and 2, a mechanism according to an embodiment of the invention allows for both translation of an object under inspection along a vertical axis as well as rotational orientation of the object about two horizontal axes, each of which is orthogonal to the vertical axis and to each other. The mechanism includes, in part, means for retaining the object under inspection. That retaining means is then guided mechanically to pivot about the two horizontal axes as well as translate along the vertical axis. The retaining means is also prevented from horizontal translational movement, as well as rotational movement about the vertical axis. Means for translating at least three distinct areas of the retaining means along the vertical axis is also provided, with those three areas being positioned so that the retaining means may be rotated about the first and second horizontal axes by the translating means.
An adjustment mechanism according to another embodiment of the invention allows for translation of an object under inspection along a vertical axis as well as rotation of the object about both the vertical axis and a horizontal axis that is orthogonal to the vertical axis. The mechanism includes, in part, means for retaining the object, and means for rotating the retaining means about the vertical axis. Means for guiding the rotating means permits the rotating means to pivot only about the horizontal axis. The guiding means and the rotating means are coupled so that they are permitted to move translationally along the vertical axis. Means for translating at least two distinct areas of the rotating means along the vertical axis is also included, with the two areas residing on opposite sides of the horizontal axis.
Another embodiment of the invention exists in the form of a method for adjusting both the location of an object along a vertical axis and the rotational orientation of the object about a first and second horizontal axes, with the first and second horizontal axes each being orthogonal to the vertical axis and to each other. The object under inspection is allowed to pivot about the first and second horizontal axes, and to translate along the vertical axis, while being prevented from either substantial translational movement in the plane defined by the first and second horizontal axes or substantial rotational movement about the vertical axis. At least three areas of the object are then translated substantially along the vertical axis, with the three areas being positioned so that the object may also be rotated about the first and second horizontal axes so that the object resides in a predetermined vertical position and rotational orientation.
Another method embodiment adjusts both the location of an object along a vertical axis and the rotational orientation of the object about the vertical axis and a horizontal axis that is orthogonal to the vertical axis. The object is allowed to rotate about a vertical axis and pivot about the horizontal axis, while being restricted with respect to other translational and rotational movement. The object is then rotated about the vertical axis, pivoted about the horizontal axis, translated along the vertical axis until the object resides in a predetermined vertical position and rotational orientation.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.